WASHINGTON – President Donald Trump said Sunday he will continue to insist on federal money for a U.S.-Mexico border wall as the partial government shutdown triggered by the barrier dispute entered its 16th day.

“It’s a very important battle to win,” Trump told reporters as he left the White House en route to a staff retreat at Camp David, casting the shutdown battle as a national security issue.

While Trump huddles with aides at Camp David, other administration officials and congressional staff members are scheduled to meet again for more negotiations to end the shutdown.

The shutdown reached a milestone on Sunday, tying for the third longest on record.

“This shutdown could end tomorrow or it also could go on for a long time,” Trump said.

Trump also repeated that he is considering some kind of national emergency declaration that would, in theory, allow him to use defense funds to start building a wall.

Democrats denounced Trump for both his wall demands and his talk of declaring an emergency.

“This would be a terrible use of department of defense dollars,” said Democratic Rep. Adam Smith of Washington, the new chairman of the House Armed Services Committee, on ABC’s “This Week.”

He also told ABC: “The president really doesn’t understand the issue.”

With the parties unable to agree on a spending plan to fund about a quarter of the federal government, Trump is insisting on more than $5 billion for a wall along the U.S.-Mexico border; Democrats, calling the wall expensive and impractical, want to reopen the government at least temporarily to provide space for more negotiations.

In speaking with reporters, Trump said he sympathizes with the hundreds of thousands of federal workers who have been furloughed or are working without pay, but they can “adjust.”

On other issues, Trump:

•  Confirmed he will give his State of the Union address on Jan. 29, pursuant to an invitation sent Thursday by new House Speaker Nancy Pelosi, D-Calif.
•  Said he hopes to meet again soon with North Korea leader Kim Jung Un over his nuclear weapons program; Trump again claimed, with no evidence, that without his diplomacy the U.S. would be at war with Kim’s nuclear-armed government.
•  Claimed he is still withdrawing U.S. troops from Syria, but won’t necessarily do so “quickly;” earlier in the day, during a trip to Israel, National Security Adviser John Bolton said the U.S. would not withdraw until Turkey pledges that it won’t attack Kurdish forces in Syria.

Before his departure for Camp David, Trump taunted Democrats over the immigration, noting that luminaries like Barack Obama and Hillary Clinton have expressed concern about illegal crossings.

“The only reason they do not want to build a Wall is that Walls Work!” Trump insisted in one tweet. “99% of our illegal Border crossings will end, crime in our Country will go way down and we will save billions of dollars a year!”

 Acting White House Chief of Staff Mick Mulvaney said the administration is willing to give up plans for a concrete wall and focus instead on a fence composed of steel slats.

“What’s driving this is the president’s desire to change the conditions at the border,” Mulvaney told NBC’s “Meet The Press.” “And if he has to give up a concrete wall, replace it with a steel fence in order to do that so that Democrats can say, ‘See? He’s not building a wall anymore,’ that should help us move in the right direction.”

Mulvaney, however, suggested the end of the shutdown is not near, telling NBC: “I think this is going to drag on a lot longer.”

Democrats called the idea of a physical barrier across the entire border expensive and ineffective, and said the solution involves more personnel and detection technology.

Now in control of the House, Democrats are focused a plan to reopen the government that would include temporary funding for the Department of Homeland Security, which handles border issues.

Funding DHS until Feb. 8 would give the parties time to negotiate a new plan for border, said House Speaker Pelosi and other Democrats.